Permanent magnets made of various metallic and metallic/rare earth alloys are well known. For example, aluminum-nickel-cobalt (AlNiCo) and samarium-cobalt alloys are used in making permanent magnets. Both AlNiCo magnets and samarium-cobalt magnets contain a high percentage of cobalt. In general, AlNiCo magnets contain more than 25% cobalt; samarium-cobalt magnets generally contain at least 25% cobalt and can contain much more. Cobalt, however, has become expensive and difficult to obtain. Cobalt deposits are not located in the United States or other nations with which the United States trades on a regular basis.
Hard magnetic materials comprising only rare earth elements and iron have been studied. However, only terbium-iron alloys show good hard magnetic properties in the amorphous and crystallized states. For example, gadolinium-iron, and yttrium-iron alloys have also been studied but do not show good hard magnetic properties. (See "Anomolous Magnetization of Amorphous TbFe.sub.2, GdFe.sub.2, and YFe.sub.2 ", J. J. Rhyne, 10 Physical Review B, No. 11, December, 1974). Other rare-earth iron alloys are also known for their hard magnetic properties. For example, one iron-boron-rare earth magnetic alloy is EQU (Fe.sub.x B.sub.1-x).sub.0.9 Tb.sub.0.05 La.sub.0.05
(Koon, et al., the "Composition Dependency of Coersive Force and Microstructure of Crystallized Amorphous (Fe.sub.x B.sub.1-x).sub.0.9 Tb.sub.0.05 La.sub.0.05 Alloys", IEEE Transaction on Magnetics MAG-18, No. 6, November, 1982 and Becker, "Surface Effects in Hysteresis Loop Shapes in High-Coercive Force Crystallized Amorphous Alloys" IEEE Transactions on Magnetics, MAG-18, No. 6, November, 1982). However, these alloys have a relatively low energy product (four to eight megagauss-Oersteds), indicating inferior hard magnetic properties. Permanent magnets made primarily of alloys of more abundant, inexpensive and non-strategic rare earth elements are desirable.
One such light rare-earth element is praseodymium. However, certain alloys which contain only praseodymium and iron have been found to have hard magnetic properties below the standards for economic viability (see, J. J. Croat "Permanent Magnet Properties of Rapidly-Quenched Rare Earth-Iron Alloys", presented at Third Joint Intermag-Magnetism and Magnetic Material Conference, Montreal, Quebec, Canada, 1982).
Neodymium is another rare earth element which is used in magnetic alloy materials. Magnetic alloys composed of neodymium, iron, and boron have been developed. Other types of alloys which do not contain cobalt have been developed. U.S. patent application Ser. No. 076,067, for example, describes certain light rare-earth, iron, boron and silicon alloys having excellent hard magnetic properties. However, it has been found that some magnetic alloys comprising neodymium, iron and boron tend to become demagnetized in an irreversible fashion when subjected to high operating temperatures, e.g., above 130.degree. C. It is expected that the Curie temperature of these materials, or the temperature at which all ferromagnetic properties disappear, would be in the range of 300.degree.-350.degree. C. A material having a Curie temperature in this range is unacceptable for use in standard industrial motors.